Amsterdam taxis are a nightmare.

A couple of years ago, they were deregulated, meaning that any old numpty can stick a 'taxi' sign on the roof, get a pair of taxi plates, and charge what they like (provided it's clearly displayed in Dutch - watch out for creeping charges over x number of kms and extortional 'eerste aanslag' - flag fall).

The dodgier ones will generally try to take you out from the centre via the Weesperplein towards the ArenA, then round the busy part of the Ring to Schiphol. This will cost you in the region of €50-60, where the more direct route via Amsterdam-West (there's a number of good routes, depending on the time or day) or by Zuid/WTC, will cost you in the region of €30-40.

The most reliable of the taxi firms is TCA - Taxi Centrale Amsterdam (STA - Schiphol Taxi Amsterdam - belong to this), and it's worth calling them directly (020 566666) to get a decent taxi, or going to one of the city-run (not 'unofficial') ranks to seek out one of their taxis.

Avoid, at all costs, 'Flash' (aka TCF) and TBA (or indeed, anything that looks a bit like TCA or STA, but isn't quite it). Don't get a taxi outside the Krasnapolsky (there is a good rank the other side of the Koninklijke Paleis) and never get one at the Damrak end of the Red Light District.

At Schiphol, you are not obliged to take the first taxi, but they are obliged to take you, even if you're headed somewhere near like Schiphol-Rijk or Hoofddorp.

Best of all, to avoid all of this, is to hire a bike (the main stations hire out very nice Batavus Railstars) or get yourself a strippenkaart and hop on the trams (or indeed the trains, if you're going to/from Schiphol).

Never let a taxi driver suggest for you to see something or go somewhere. They will most likely take you to a place where they get a kickback. Ive heard stories of people being taken to shops with outrageous prices, restaurants that are lesser quality, or even strip clubs for a free "drink" then the second drink costs like $100, but you never see the menu. There are a lot of crooks out there who are not bad people, but just trying to make a buck. Tourists are an easy target for them.

What are some other horror stories that people have had? This is a great and informative thread!

On my first day in India I took a taxi from my hotel to the Red Fort. On the way back, the driver stopped at a souvenir shop. It was one with the official government insignia (well, it LOOKED official) and I ended up buying a salwar kameez (the local tunic-style outfit), a tablecloth and a silk scarf. They were VERY eager to show me anything- I could see their eyes light up when I expressed interest in jewelry, although I didn't buy any. (I've since bought some beautiful pieces at shops my local colleagues recommended.)

What I bought was good stuff and as I type this, the tablecloth is on my dining room table 7 years later- but it was only later that it occurred to me the taxi driver probably got a nice cut!

I should also mention before people who know India correct me- I was handed off to a bicycle rickshaw driver as we got to an area closed off to car traffic. He took me around theRed Fort so I could get the whole view, and was waiting when I came back after exploring it. He didn't ask for money till he'd deposited me back with the taxi driver and I paid him the upper range of what the taxi driver suggested. First trip to India, first day on the ground, and an unexpected handoff to a bicycle rickshaw piloted by a guy who didn't speak English. THAT was a leap of faith! I'm grateful it turned out well.

Not sure how accurate this is worldwide. Seems fairly accurate for US cities I have tried.
http://www.taxifarefinder.com/

Should give you at least a ballpark fare so you don't get totally ripped off.

In the poorer parts of Asia (such as Cambodia), there's a variation on this. You walk out of your hotel, intending to walk around town and see the sights on foot. At least half a dozen taxi and tuk-tuk drivers standing outside the door will ask you if you want a ride. As you walk away from the hotel, others standing nearby will join in, even though they've just seen you refuse half a dozen of their competitors who offer the exact same service at the exact same price. I have no idea why they think you'd chose them after turning down everyone else.

If you have a smartphone, follow along on Google Maps. If you see the driver deviating from the obvious route, challenge them. If they have an honest reason (which they almost always do), they'll be happy to explain their choice of route.